The present invention relates to a new and improved method of manure processing to enhance conditions in a facility for raising swine (sus scrofa domesticus) and to improve environmental effects from the swine manure generated at these facilities. More specifically, the present invention relates to controlling ammonia volatilization and odors in a swine rearing facilities, as well as controlling non-point source phosphorus runoff originating from swine lagoon effluent or liquid hog manure.
Different construction designs are known for rearing facilities on swine farms. One conventional type includes a floor which includes a grate or slatted section. Manure from the swine falls through the grate into a manure collection pit. The manure must be periodically cleaned out from the pit. Another more modern type of facility includes a floor, such as a concrete floor, which has at least one flushing trough or channel defined in the floor. Manure temporarily collects on a portion of the floor, e.g., in the trough, but the trough is periodically flushed with flush water to wash the manure down through the trough to an anaerobic lagoon or holding pond. In this latter type of facility, a typical flushing system removes all of the accumulated manure every 8 to 12 hours.
Most large-scale hog rearing facilities are totally roofed confinement systems in which no absorbent bedding material is used, permitting the manure to be efficiently handled as a slurry or as a liquid. Liquid manure is significantly diluted with water to assist in transporting and applying the manure, but relatively little water is added to the excreted manure and urine in a slurry manure system.
In the aforementioned types of facilities, the accumulation of manure results in the production of ammonia gas from ammonia volatilization. This atmospheric ammonia can be produced in relatively high quantities. The water used for flushing swine facilities is typically recycled from waste storage ponds or lagoons. Nitrogen in swine lagoon effluent is mostly in the form of NH.sub.4, with little of the NO.sub.3 form present. The remainder of the nitrogen present is bound in organic forms. Ammonia concentrations of 350 mg/l and greater are common in lagoon effluent. In addition, swine lagoon pH values are commonly in the alkaline range (pH&gt;7.0), so ammonia (NH.sub.3) is favored over NH.sub.4, resulting in conditions favorable for ammonia volatilization. When this high pH water is used for flush water, large quantities of ammonia are volatilized, causing elevated levels of ammonia gas in the atmosphere.
Studies reveal that high atmospheric ammonia levels in swine rearing facilities substantially impede feed consumption and average daily weight gain in pigs. High levels of atmospheric ammonia in swine rearing facilities have been shown to aggravate swine respiratory problems, increasing their susceptibility to micro-organisms responsible for such respiratory problems. It has been found that ammonia also increases the susceptibility of four week old pigs to conceal atrophy. Likewise, it has also been shown that high ammonia levels in swine facilities may play a significant role in the development of atrophic rhinitis. For these reasons, it is desirable to reduce the amount of ammonia gas generated within hog rearing facilities.
Ammonia (NH.sub.3) volatilization from hog manure is also detrimental to the environment due to its effect on acid rain deposition. Studies indicate that atmospheric ammonia pollution plays an important role in acid rain pollution. In Europe, the dominant source of atmospheric ammonia has been found to be livestock wastes, with long-term trends showing a 50% increase in ammonia emissions in Europe between 1950 to 1980. Ammonia raises the pH of rainwater, allowing more SO.sub.2 to dissolve in it, eventually forming ammonium sulfate, which releases nitric and sulfuric acid in soils upon oxidation. Experts believe that this produces two to five times the acid input to soils previously described for acid atmospheric deposition, resulting in extremely low pH values (2.8-3.5) and high levels of dissolved aluminum in non-calcareous soils.
Ammonia volatilization also greatly increases atmospheric N fallout, which contributes to eutrophication. Nitrogen deposited by wet fallout tripled in Denmark between 1955 to 1980 and corresponded to N losses from agriculture during the same period. Rising levels of N in the fallout have also been shown to be highly correlated to the NO.sub.3 form nitrogen content in Danish streams.
Atmospheric ammonia can also result in the formation of ammonium nitrate particles in the air. These particles, which are usually less than two microns in size, contribute greatly to small airborne particles referred to as PM.sub.10 's (particulate matter less than 10 microns).
Swine production is a growing industry in the United States, and the industry is building increasing numbers of the above-described swine rearing facilities in watersheds susceptible to eutrophication. As a result, various groups have expressed concern over eutrophication problems associated with traditional handling of swine manure.
In particular, modern swine rearing facilities often have high numbers of animals, but many have a relatively limited land base over which the manure may be applied. This leads to an over-application of nutrients, especially phosphorus, to the soil. Phosphorus is considered to be the primary element of concern with respect to eutrophication of freshwater systems. The threat of eutrophication due to phosphorus runoff has resulted in limits being placed on the amount of animal units produced per area of land in The Netherlands.
Accordingly, new facilities and methods are needed for rearing animals under conditions which reduce ammonia volatilization, to prevent nitrogen losses in order to improve the fertilizer value of manure to be used as an agricultural fertilizer, and to reduce the soluble phosphorus content of the manure to prevent phosphorus runoff from fields fertilized by swine manure.